Method of forming a notch in a bobbin case carrier



April 30, 1963 L. J. KUHAR 3,087,388

METHOD OF FORMING A NOTCH IN A BOBBIN CASE CARRIER Original Filed May 19, 1958 INVENTOR. Ludwig J. Kuhar PRIPRART /5M ATTORNEY United States Patent 3,087,388 METHOD OF FORMING A NOTCH IN A BOBBIN CASE CARRIER Ludwig J. Kuhar, Clark, N.J., assignor to The Singer Manufacturing Company, Elizabeth, N.J., a corporation of New Jersey Original application May 19, 1958, Ser. No. 736,160, now Patent No. 3,046,922, dated July 31, 1962. Divided and this application Aug. 2, 1961, Ser. No. 128,780

1 Claim. (CI. 90-11) This application is a division of application Serial No. 736,160, tfi'led May 19, 1958 and now Patent No. 3,046,922.

The present invention relates to a bobbin case carrier of a sewing machine and more particularly to the dormation of the rotation restraining notch in the bobbin case carrier of a sewing machine.

In a lock stitch sewing machine of the rotary hook type, the bobbin is mounted in a bobbin case that is in turn inserted in a bobbin case carrier which mounted in the body of the rotary hook for rotation of the hook relatively to the bobbin case carrier. During operation of the sewing machine, the bobbin case carrier is restrained against rotation while the hook is rotated relatively thereto to seize and cast a loopof needle thread about the bobbin case carrier. Since the needle thread loop must pass completely around the bobbin case carrier, the rotation restraining means must allow for passage of the thread between the rotation restraining means and the bobbin case carrier. In the conventional manner, the rotation restraining means comprises a finger mounted in the bed of the machine and having a tongue that is seated in a notch in the face of the bobbin case carrier. This invention relates specifically to the formation of this rotation restraining notch in the bobbin case carrier and has for an object to torm this notch in such a manner as to facilitate manutfiacture.

Having in mind the above and other objects that will be evident from an understanding of this disclosure, the invention comprises the devices, combinations and arrangements of parts as illustrated in the presently preferred embodiment of the invention which is hereinafter set forth in such detail as to enable those skilled in the art readily to understand the function, operation, construction and advantages of it when read in conjunction with the accompanying drawings in which:

FIG. 1 is a plan View of a bobbin case carrier for a rotary book of a sewing machine, which bobbin case carrier embodies the present invention.

'FIG. 2 is a fragmentary sectional view taken substantially on the line 2-2 of FIG. 1,

FIG. 3 is a fragmentary plan view similar to FIG. 1 and illustrating the prior art.

The present invention is herein disclosed as applied to a bobbin case carrier of a conventional type of rotary hook which is illustrated, for example, in the United States patent of Kessler, No. 2,085,699, to which reference may be had for an understanding of the function and operation of the bobbin case carrier.

As illustrated in the drawings, the bobbin case carrier is cup-shaped and comprises a cylindrical side wall 1 which, to reduce the mass, has an ope-n back that is spanned by a diameter bar 2. The bar 2 supports a centrally located stud 3 for mounting and latching the bobbin case within the carrier.

For journaling the bobbin case carrier within the raceway of a rotary book, there is provided a peripheral bearing rib 4 on the outer surface of the side wall 1. The bearing rib 4 is discontinuous to provide a thread loop detaining shoulder 5- and a loop confining shoulder 6. On the needle thread loop cast off side, there is provided ice on the top of the side wall 1, a laterally extending loop controlling flange 7 that extends beyond the top center of the carrier and at the top thereof is provided with a notch 8 for receiving the tongue of a rotation restraining finger (not shown). On the cast on side of the bobbin case carrier, there is provided a bobbin thread guiding slot 9. The rear face of the flange 7 at the top thereof is milled away at 10 and has a bore 11 to provide for needle clearance. I

With reference to FIG. 3, there is illustrated a bobbin case carrier construction in accordance with the prior art methods and which includes I3. rotation restraining notch 8a. In the prior construction, the rotation restraining notch 8a was formed in three successive milling operations. In the first operation, a slot is milled in the face of the flange 7 by a relatively wide cutter that passes straight across the face of the flange 7 substantially radially of the bobbin case carrier, thus producing the side walls 12 and the bottom 13' of the notch 8a. To avoid the sharp corners of the inner end of the side walls 12 that result from the first milling operation, over which corners the thread is drawn during the sewing operation, the inner ends of the side walls 12 were flared or beveled outwardly by means of relatively narrow cutters in the two subsequent milling operations. These cutters were passed through the slot at an angle to the center line of the slot, thus producing the side walls '14 and 15 and the respective bottoms 16 and 17.

Within the limitations of reasonably economical manufacturing processes, the cutters in the milling operations cannot be held to exactly the same depths with the result that the bottoms 13, 16 and 17 do not coincide, or in other words, do not define a single continuous planar bottom for the notch 81:. In FIG. 3, there is illustrated the condition that results when the left hand cutter is set at a depth slightly less than the depth of the initial straight cutter and the right hand cutter is set at a depth slightly greater than the depth of the initial cutter. In this case, the bottom 16 is above the bottom 13' with a resulting edge 18 at the meeting line, and the bottom 17 is below the bottom 13 and in effect cuts a groove in the bottom 13 which produces edges 19.

Since during the sewing operation, the limb of the needle thread must be swung laterally across the notch 8a before the loop is withdrawn, the bottom of the notch 8a must be smooth and continuous, or in other words, without edges such as at 18 and 19 upon which the thread could catch or snag and be thus held back. Thus, after milling in the prior construction, the bottom of the notch 8a had to be hand filed to remove any edges, such as 18 and 19, resulting from the milling operations. Because the notch 8a is only less than one eighth of an inch wide and because the post 3 is located only three eighths of an inch trorn the inner edge of the side wall 1, this filing operation is very delicate and difiicult. At the same time, and also because of the variations in the resulting edges in the bottom of the notch So, this filing operation was performed by hand. It is obvious that finishing of the bottom of the notch 81: was an expensive operation.

In accordance with the present invention there has been provided a bobbin case carrier in which the rotation restraining notch S is forrnedin such a manner as to eliminate the subsequent hand filing that is required in the prior art construction. As illustrated in FIGS. 1 and 2, the notch '8 in the present construction comprises an outer portion 20 in the form of a slot having parallel side walls 21 and a planar bottom 22. The outer portion 20, like the slot formed in the first milling operation in the prior art construction, is arranged substantially radially of the bobbin case carrier. To flare the inner ends of the slot outwardly there is an inner portion 23 comprising a depression milled in the face of the flange 7 to substantially the same depth as the outer portion 20 and having an inner edge which is defined by the coinciding inner edges of the side Wall 1 and flange 7 and an outer edge which is arouate with a diameter greater than the width or" the 10111161 portion 20 and arranged substantially centrally of the center line of the outer portion 20. The inner portion 23 is thus crescent-shaped and intersects the side Walls 21 of the outer portion 20 to provide arcuate side edges 24 which constitute diverging side walls and thus act to flare outwardly the inner ends of the side Walls 21 of the outer portion 20. The inner portion 23 includes a bottom 25 which, to avoid a sharp edge :at its meeting line with the bottont wall 22 is amanged at -a slight angle to the plane of the bottom wall 22, the angle being illustrated at A in FIG. 2 and being substantially three degrees. Thus, the bottom walls 22 and 25 will always intersect along a line, such as 26, and will blend smoothly.

In the formation of the slot 8 in accordance with the present invention, the first operation is the same as in the prior construction, -i.e., the flange 7 is first milled by a cutter that passes across the face thereof to provide a slot and thus form the outer portion 20 of the notch 8 The slot is then flared, as illustrated in FIG. 2, by a circular end mill 27 [having a diameter greater than the diameter of the slot and advanced endwise onto said flange with the axis thereof arranged at an angle of three degrees to a line normal to the bottom wall 22 to formthe inner portion 23 of the notch =8. Thus, the notch 8 has been completely formed in only two operations and Without the necessity of a subsequent hand filing operation. Any

variations in the depth of penetration \of the end mill 27 from the designed optimum, while it may vary the position of the line 26 radially of the bobbin case carrier or may produce an edge along the line 26, it does not produce any appreciable edges lengthwise of the notch 8 upon which the thread could snag as it moves laterally of the notch 8.

Numerous alterations of the structure herein disclosed will suggest themselves to those skilled in the art. However, it is to be understood that the present disclosure relates to a preferred embodimentof my invention which is for purposes of illustration only and not to be construed as a limitation of the invention. All such modifications which do not depart from the spirit of the invention are intended to be included Within the scope of the appended claim.

Having thus set forth the nature of the invention, what I claim herein is:

The method of forming a rotation restraining notch in a sewing machine bobbin case carrier having a cylindrical side Wall and a laterally extending flange on the top of said side Wall, comprising the step of cutting a slot across the face of said flange arranged generally radially of said bobbin face carrier and having a planar bottom and parallel side Walls, and the step of flaring the inner ends of said side Walls by a circular end cutter havinga diameter greater than the width of said slot and advanced endwise onto said flange at the \inner end of said slot at a slight angle to a line normal to the bottom of said slot.

No references cited. 

